The serial data line is the means by which the microprocessor
controlled modules in the vehicle communicate with other control modules and
the scan tool. There are two different types of communications used on
this vehicle:
The class 2 data line is powered by the modules that are connected to
it during operation. Communication on the Class 2 data line occurs on an
as needed basis, rather than being a continuous stream of data. Information
is transmitted in bits, with each bit indicating status that is either low
(0 volts) or high (7 volts). When no communication is occurring
on the Class 2 data line, voltage is low.
Class 2 data is transmitted at a higher speed and messages are configured
differently than UART data. While UART uses a master to control serial data
line traffic, Class 2 uses the peer to peer method along with message arbitration
to manage data line traffic.
The control modules on the Class 2 data line are as follows:
| • | The body control module (BCM) |
| • | The transfer case control module (TCCM) |
| • | The vehicle control module (VCM) |
| • | The electronic brake control module (EBCM) |
| • | The electronic climate control (ECC) module |
The inflatable restraint sensing and diagnostic module is the only module
on the UART data line.
